Metal cans, as one form of food packaging containers are excellent in mechanical strength and long-term preservability, can be packed with high-temperature contents as they are and can be hermetically sealed, can be easily subjected to sterilization treatment such as retort sterilization treatment after the hermetic sealing, and are thus highly safe and hygienic as packaging containers. Metal cans have the advantage that they are easily separated and collected from wastes. Metal cans have been conventionally manufactured from coated metal sheets, in which coating processes performed in can manufacturers are, however, complicated and low in productivity. In addition, when a solvent-based coating material is used, a large amount of solvents volatilizes in drying and baking treatment performed after coating, and environmental problems such as discharge of solvents occur. Furthermore, in order to avoid adverse effects of solvents on human bodies, there is a growing move to restrict bisphenol A (BPA) as a type of environmental hormones contained in a coating material.
In view of such a background, in recent years laminated metal sheets with a BPA-free thermoplastic resin film thermally fusion-bonded to a metal sheet surface have been used as a metal can material. Laminated metal sheets with a polyester resin film thermally fusion-bonded to a metal sheet surface in particular are excellent in performance in terms of food sanitation and are thus widely used. Specifically, the laminated metal sheets with a polyester resin film thermally fusion-bonded to a metal surface are used for lids, drawn and redrawn (DRD) cans, drawn and ironed (DI) cans, or the like. The DRD cans and the DI cans have a high degree of processing, and when the laminated metal sheets are used for the DRD cans or the DI cans, the polyester resin film is required to have excellent formability. In view of such a background, Patent Literature 1 and Patent Literature 2, for example, disclose a technique in which a biaxially oriented polyethylene terephthalate film is laminated onto a metal sheet through an adhesive layer formed of a low melting point polyester, which is used as a metal can material. Patent Literature 3 and Patent Literature 4 disclose a method that manufactures a laminated metal sheet and a metal can body with a high drawing ratio using a thermally fusion-bondable polyester resin film.